The crystalline lens of the eye is one of the structures that are essential to vision. In a healthy eye, the lens is a transparent, biconvex structure that refracts light to form an image on the retina. The lens also functions to change the focal distance of the eye by changing shape, so that it can focus on objects at various distances, thereby forming a sharp image of an object on the retina. This process is called accommodation.
Unfortunately, the lens is often subject to age-related damage. For example, a cataract is an often age-related clouding of the lens inside the eye that leads to a decrease in vision. It is the most common cause of blindness and is conventionally treated with surgery. Visual loss from a cataract occurs because opacification of the lens obstructs light from passing and being focused on to the retina at the back of the eye. Although a cataract is most commonly due to aging, for example, that degrades the lens proteins over time, there are many other causes as well.
More specifically, a cataract is formed of a yellow-brown pigment that is deposited within the lens and which, together with disruption of the structure of the lens fibers, leads to reduced transmission of light, which in turn leads to visual problems. Those with cataracts commonly experience difficulty discerning colors, changes in contrast, driving, reading, recognizing faces, and may have problems with glare from bright lights.
Cataracts can be addressed using surgical procedures. Almost all cataract patients' vision can be improved by surgery, with well over 90% of surgical patients achieving a corrected vision of 20/40 or better. Most commonly, cataract surgery is performed using a procedure called phacoemulsification, which uses a hand-held probe or handpiece coupled to a console. In general, no part of the probe or the console comes into contact with any part of a patient's tissues, fluids, or the like, except for the needle of the handpiece. Typically, all elements of a phacoemulsification system that come into physical contact with the patient's tissues are discarded and replaced before the system is used for another operation. The replacement parts, as well as other supplies used during the operation, are typically provided in a so-called phaco pack.
Cataract surgery involves breaking up and/or liquefying the natural lens in a process called emulsification, aspirating the emulsified lens, and irrigating the eye during the procedure. However, although important to surgical outcome, the aspiration flow rate and irrigation flow rate during surgery is not presently directly measured during surgery because of the invasive nature of flow rate detection methods, which can cause unwanted complications.
Thus, a need exists to directly measure the aspiration and irrigation flow rates during phacoemulsification surgery while mitigating the adverse effects that attend the prior art.